1. Field of the Invention
The invention relates to optical filters.
2. Related Prior Art
Volume reflection grating filters have been proposed for use in wavelength multiplexed optical systems. An example of such a filter is described in published U.K. Patent Application GB No. 2151036. However, such reflection filters are difficult to implement in practice since an incident light beam is reflected back towards the launch direction making it difficult to couple the filtered wavelength into a detector or other output device. Furthermore, with reflection filters, once a desired wavelength has been selected by the grating, the filtered wavelength must generally be separately focussed into an output optical fiber for onward transmission.